As blood circulates throughout the body, it delivers different nutrients and oxygen and removes waste. Numerous blood cells characterize the physiological condition of the body and changes in the quantity and condition of blood cells can result in disease;​ thus, the isolation of certain blood cells can aid in the diagnosis and treatment of various diseases.

Conventional techniques for blood cell separation are time-consuming, costly, and can result in morphological changes due to high shear stress. Innovative lab-on-a-chip-based separation techniques have been utilized to solve these issues. Acoustofluidics (i.e., a coupling of microfluidics and acoustics) has been one of the most effective approaches for separating cells, EVs, and synthetic microparticles among the different methods introduced. In contrast to conventional separation procedures used in clinical laboratories, which are focused on chemical qualities, the acoustofluidic process depends on the sample's physical properties. Studies working on blood cell separation using acoustophoretic technique are mostly limited to separation/purifying RBC and Platelets. In contrast, the separation of different subtypes of WBCs has not been investigated thoroughly since the cutoff size of different types of white blood cells is narrow. Thus, separating such cells requires enhanced precision, significantly if the method used is only sized-based. This work studies the potential of using a two-stage parallel standing surface acoustic wave (paSSAW) acoustofluidic platforms in separating microparticles with small cutoff sizes. The first stage of the device employs a combination of acoustic and hydrodynamic focusing mechanisms to boost the alignment efficiency prior to the second stage. The second module of the device separates the microparticles using a paSSAW acoustofluidics platform. In this thesis, a three-dimensional numerical simulation has been developed to maximize the performance of the platforms mentioned above and study the effect of different design parameters on the precision of the separation. The numerical results were then validated by a subsequent experimental study. In complete agreement with the numerical result, the developed platform achieved a high-resolution separation of 2 µm cutoff size where 10µm and 8µm diameter polystyrene microparticles were successfully separated with an accepted rate of purity of >​80%.